A cross-sectional study in humans and a longitudinal investigation in monkeys is proposed a study local host mechanisms involved in the initiation and progression of periodontitis. Humans with periodontal disease of varying severity will be studied with regard to gingival neutrophil function, gingival fluid antibodies reactive with antigens of periodontal disease-associated bacteria, and gingival fluid complement cleavage products. These local host mechanisms will also be studied longitudinally during the initiation and progression of ligature-induced periodontitis in monkeys. Additionally, in vitro studies of the effects of certain periodontal disease-associated bacteria and their products on normal neutrophil function will be conducted. This proposal will apply information gained from previous studies of systemic manifestations of the host response to a direct investigation of possible local pathogenic mechanisms occurring within the disease site. Emphasis will be placed both on possible immunopathologic effects of bacterial products and on the ability of these products to alter normal host defense mechanisms.